With regard to the TRB classification system for the mixture, the percentage of cement, in relation to the dry unit weight of soil or alternative materials, necessary to obtain a stable soil-cement mixture with minimal mechanical strength in compliance with the technical requirements of structural projects for base layers of flexible pavements must initially be in the order of 7% according to the technical standard NBR 12253 (Associacao Brasileira de Normas Tecnicas [ABNT], 2012c).
The mixture composed of 60% flotation tailings and 40% magnetic concentration tailings, in relation to the dry unit weight of the mixture 03, has the higher bearing capacity (Table 2).
Regarding the maximum apparent dry unit weight, it was expected lower values for granulometrically finer mixtures.
Optimum moisture content of cohesive soils increases whereas the maximum dry unit weight obtained through compaction tests decreases with plasticity index of soil (Berawala, Solanki 2010; Pandian et al.
--Due to chemical reaction between contaminant and soil particles, soil becomes more plastic in nature which causes a decrease in maximum dry unit weight and an increase in optimum moisture content.
Variation of maximum dry unit weight with effluent contamination
Similar trend was followed by the relationship between unconfined compressive strength and dry unit weight of soil as shown in figure 4 (a,b).
Unconfined compressive strength can be best predicted using moisture content and dry unit weight.
Independent variables consisted of parameters related to grain size distribution which included mean grain size (D50) effective grain size (D10) uniformity coefficient (Cu) curvature coefficient (Cc) fine contents (F200) and dry unit weight of the remolded samples.
As indicated by regression analysis mean grain size (D50) curvature coefficient (Cc) and dry unit weight have a significant effect on internal friction angle of sandy soil as compared with other input parameters.
Based on the experimental data correlation of internal friction angle with dry unit weight (d) mean grain size (D50) and coefficient of curvature (Cc) have been proposed.
This can be explained that, as the maximum dry unit weight increases at 1% by weight, the soil becomes denser due to void filling by this material and consequently yields at a higher load.
The highest maximum dry unit weight value was obtained for the addition of 1% by weight olive waste ash.
Table 1: Physical properties of Cornell sand [D.sub.10] 0.2 mm [D.sub.50] 0.7 mm [D.sub.60] 0.9 mm Cu 4.6 Cc 0.9 Classification SP Optimum water content 10.1% Specific gravity, Gs 2.71 Maximum dry unit
weight, dry_max 17.4 kN/[m.sup.3] Table 2: Experimental condition of Sand Test 1 Test 2 Test 3 Water content, w (%) 0.5 3.1 3.4 Wet unit weight, wet (kN/[m.sup.3] 18.4 17.0 16.7 Dry unit
weight, dry (kN/[m.sup.3] 18.3 16.6 16.2 Friction angle from slow triaxial 49 40 39 compression test (0.1%/min), TXC-0.1 (degree) Friction angle from Fast Triaxial 51 43 42 Compression test (5%/min), TXC-5 (degree) Table 3: Experimental Results Test 1 Test 2 Test 3 Ground displacement at leak, 0.78 0.85 ?
The system uses separate distillation, wash and dry units
, as well as a steam generator and nitrogen generator.